1. Field of the Invention
The present invention relates to the field of keyboards.
2. Prior Art
Photo-optical keyboards of various types are known in the prior art. By way of example, certain types of keyboards are shown in U.S. Pat. No. 3,856,127. The primary embodiment disclosed in that patent has a plurality of light channels arranged in rows and columns with light sources at one end of each channel and photodetectors at the other end thereof. The channels forming the rows have a different depth than the channels forming the columns, with each key having two shutters coupled thereto disposed adjacent rather than on an intersection of the two channels so that each shutter may block one of the adjacent channels. Accordingly, depression of any given key will cause one shutter coupled thereto to block one light channel row whereas the other shutter will block one light channel column. Thus, a key may be identified by the particular row and column which is blocked by the depression of any given key. The system has the advantage that one light source and one detector is not required for every key, though has certain disadvantages with respect to cost and operation. The required light channels are relatively expensive to fabricate, and no means is disclosed for handling the case of simultaneous key depression. In fact, because of small differences in shutters, light channels, light sources, detectors, etc. the partial depression of two keys not disposed on the same row or column may be interpreted as the depression of a third key generally positioned at the intersection of the rows and columns, since one shutter of one key may block one row and the opposite shutter of the other key block the associated channel. Further, even if the depression of both keys is detected, no means is disposed to determine which key was depressed first or which key is released first. Other embodiments include reflectors on each key operating at the junction of the channels so that each key will reflect row light sources to column light detectors. In such a system, it is stated that a scanning means should be used, though details thereof are not given. Still other embodiments disclosed therein include a fiber-optic type device.
Other photo-optical keyboards or key-sensing systems are disclosed in U.S. Pat. Nos. 3,603,982; 3,648,050; 3,737,668 and 3,750,150. These systems, however, are entirely different from the present invention and generally lack the simplicity in design and flexibility and reliability in operation that the present invention provides.